The invention concerns a process for the separation of aromates from hydrocarbon mixtures of optional aromate i.e. aromatic hydrocarbons content, employing N-substituted morpholine, the substitutions of which display no more than seven carbon atoms, as selective solvent, by delivering only a part of the required total amount of solvent to the uppermost plate of the extractive distillation column.
The above-described general technique for the recovery of aromates has already been known for many years, and has been well authenticated in the meantime in practice at various large-scale technical plants, particularly using N-formylmorpholine as selective solvent. As indicated from German Patent DE-PS No. 15 68 940, the sump product discharged from the extractive distillation column is normally introduced to a subsequently disposed distilling column, in which the aromates contained therein as extract are distillatively separated from the solvent. The solvent is then discharged from the sump of the distilling column and led back into the extractive distillation column for re-employment. Herewith, the introduction or re-introduction of the solvent follows as a rule at the uppermost plate(s) of the extractive distillation column. The non-aromatic hydrocarbons are, on the other hand, discharged from the top of the extractive distillation column, and can be condensed partially or completely in subsequently disposed condensation arrangements. A variation of this manner of operation is known, moreover, from German Patent DE-PS No. 20 35 771, in which only a part of the selective solvent is delivered to the uppermost plate of the extractive distillation column, while the rest of the solvent, together with the entry product, is introduced into the extractive distillation column by means of the conduit provided for the introduction of entry product.
Whether or not the above-described techniques, as already stated, have been well authenticated in practice, it has remained desirable to optimize further this manner of operation and, indeed, particularly with regard to an increase in the throughput capacity and a more silent operation of the extractive distillation column, as well as an improvement in the results.
In pursuance of this object, it has now surprisingly been discovered that with a technique of the above-described type, such an optimization can be obtained when according to the present invention the part of the total amount of the solvent which is not delivered to the uppermost plate of the extractive distillation column, amounting to between about 10 and 40 percent by weight, distributed into at least two partial streams, is introduced into the extractive distillation column onto plate above the inlet for the hydrocarbon mixtures, and further so adjusting the delivery temperature of the respective partial streams of solvent that they do not exceed the temperature of the corresponding feed plates and also fall no more than 10.degree. C. below said temperature.